net: usb: ax88179_178a: move priv to driver_priv

We need more space to save WoL context. So lets allocate memory
for ax88179_data instead of using struct usbnet data field which
only supports 5 words. We continue to use the struct usbnet data
field for multicast filters. However since we no longer have the
private data stored there, we can shift it to the beginning.

Signed-off-by: Justin Chen <justinpopo6@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>